calculate agent.conf path from self.unit.name

src/charm.py

@@ -56,7 +56,7 @@ def _on_dashboard_relation_joined(self, event):
     def _on_website_relation_joined(self, event):
         """Connect a website relation."""
         logger.info("got a new website relation: %r", event)
-        port = api_port()
+        port = self.api_port()
         if port is None:
             logger.error("machine does not appear to be a controller")
             self.unit.status = BlockedStatus('machine does not appear to be a controller')
@@ -90,7 +90,7 @@ def _on_metrics_endpoint_relation_created(self, event: RelationJoinedEvent):
                     "password": password,
                 },
                 "tls_config": {
-                    "ca_file": ca_cert(),
+                    "ca_file": self.ca_cert(),
                     "server_name": "juju-apiserver",
                 },
             }],
@@ -103,29 +103,29 @@ def _on_metrics_endpoint_relation_broken(self, event: RelationDepartedEvent):
         self.control_socket.remove_metrics_user(username)
 
 
-def _agent_conf(key: str):
-    '''
-    _agent_conf reads a value from the agent.conf file on disk.
-    If the machine does not appear to be a Juju controller, then None is
-    returned.
-    '''
-    # TODO: get the unit number/name from an environment variable?
-    path = '/var/lib/juju/agents/unit-controller-0/agent.conf'
-    with open(path) as f:
-        params = yaml.safe_load(f)
-    return params.get(key)
+    def _agent_conf(self, key: str):
+        '''
+        _agent_conf reads a value from the agent.conf file on disk.
+        '''
+        unit_name = self.unit.name.replace('/', '-')
+        agent_conf_path = f'/var/lib/juju/agents/unit-{unit_name}/agent.conf'
 
-def api_port() -> str:
-    '''
-    api_port returns the port on which the controller API server is listening.
-    '''
-    return _agent_conf('apiport')
+        with open(agent_conf_path) as agent_conf_file:
+            agent_conf = yaml.safe_load(agent_conf_file)
+            return agent_conf.get(key)
+
+    def api_port(self) -> str:
+        '''
+        api_port returns the port on which the controller API server is listening.
+        '''
+        return self._agent_conf('apiport')
+
+    def ca_cert(self) -> str:
+        '''
+        ca_cert returns the controller's CA certificate.
+        '''
+        return self._agent_conf('cacert')
 
-def ca_cert() -> str:
-    '''
-    ca_cert returns the controller's CA certificate.
-    '''
-    return _agent_conf('cacert')
 
 def metrics_username(relation: Relation) -> str:
     '''